1. Field of the Invention
The present invention relates to a method, system, and program for executing data transfer requests.
2. Description of the Related Art
In storage environments, data access commands are communicated from a host system to a storage controller, which manages access to the disks. The storage controller may be a card inside the host system or a separate device. The Internet Small Computer Systems Interface (iSCSI) protocol is used for storage networks that utilize Ethernet connections, including Ethernet switches and routers. The term “iSCSI” as used herein refers to the syntax and semantic of the iSCSI protocol defined by the IETF (Internet Engineering Task Force) standards body, and any variant of that protocol. In current storage networks where iSCSI is utilized, the packet configuration comprises an Ethernet package encapsulating an Internet Protocol (IP) and Transmission Control Protocol (TCP) package layers, which further encapsulate an iSCSI package that includes one or more SCSI commands. The Ethernet protocol provides for link-level error checking as the packets flow from point-to-point on any network segment (link) to determine whether data has been corrupted while passing on a link. In network data transmission operations, an initiator device transmits data or commands over the network to a target device. The TCP/IP package includes an error detection code to perform an end-to-end checking to determine at the opposite end whether the transmitted packet has changed during the transmission as the packet passes through switches and routers. A receiving device detecting an error will send a negative acknowledgment to the sending device to request retransmission of those packets in which errors were detected.
The Remote Direct Memory Access (RMDA) protocol provides the capability of one computer to directly place information in another computer's memory with minimal demands on memory bus bandwidth and processor overhead. RDMA over TCP/IP (also known as iWARP) defines the interoperable protocols to support RDMA operations over standard TCP/IP networks. An RDMA Network Interface Card (RNIC) network adaptor card implements the RDMA protocol and performs RDMA operations to transfer data to local and remote memories. Further details of the RDMA protocol are described in the specifications entitled “RDMA Protocol Verbs Specification (Version 1.0)”, published by the RDMA Consortium (April, 2003); “Direct Data Placement over Reliable Transports (Version 1.0)”, published by RDMA Consortium (October 2002); and “Marker PDU Aligned Framing for TCP Specification (Version 1.0)”, published by the RDMA Consortium (October 2002), and which specifications are incorporated herein by reference in their entirety.
One specification entitled “iSCSI Extensions for RDMA Specification (Version 1.0), by Michael Ko et al., released by the RDMA Consortium (July, 2003), which specification is incorporated herein in its entirety, defines a protocol for providing the RDMA data transfer capabilities to iSCSI by layering iSCSI on top of RDMA.
Data transfer systems, including the RDMA and others described above, typically require the intervention of kernel mode processes to handle the read and write operations to and from the storage devices.